"A PhD is safer. If you don’t do so well, you are going to get the title anyways. A Startup is riskier. If you don’t do very well (90% of the time), you can end broke."
Plenty of people drop out without finishing their PhD and generally they are broke afterwards. I'd say a startup is safer as you are closer to industry in case you need to find a job.
I also disagree with the author's point that a Ph.D. is about changing the world. My seven years of hard work culminated in a thesis that had a negligible impact on the universe. Many of my friends justifiably felt the same way. I set out with the intention of making the world a better place, but reality had other ideas. It's hard to see how spending those seven years at a startup company could have been worse in that respect.
I was working for a big tech firm in Silicon Valley in late 2000. I was looking for a career change so I applied to a few startups including Google. The Google recruiter called me repeatedly to come in for an interview, but I decided to quit the job search and pursue a PhD instead.
Studying for a PhD was fun, but I couldn't adjust to the lower income. I'd been working in industry for the previous five years so it was a 80% drop in income at least. Plus I got married and had a kid in those two years. That complicated things considerably.
I believe the author is suggesting that the person starts their own startup, not going to work for one. I would suggest in that case theere would be a considerable drop in income also.